Novel insights from adaptor protein 3 complex deficiency
ABSTRACT Hermansky-Pudlak type 2 is an autosomal recessive disorder characterized by oculocutaneous albinism, bleeding disorders, recurrent infections, and moderate/severe neutropenia. The disease is caused by mutations in the AP3B1 gene encoding for the beta3A subunit of the adaptor protein 3 (AP-3) complex. Because the expression of the beta3A subunit is normally ubiquitous, its deficiency leads to a precise phenotype in cells with a large number of intracellular granules, such as neutrophils, natural killer cells, cytotoxic T lymphocytes, platelets, and melanocytes. Given the AP-3 deficiency, the lysosomal membrane proteins are not appropriately sorted to the granules but are delivered to plasma membrane with subsequent effects on cell development and differentiation. Missorting of proteins (eg, tyrosinase) in melanocytes and platelets accounts for oculocutaneous albinism and bleeding disorders, respectively. Absence of AP-3 leads to low intracellular content of neutrophil elastase and consequently to neutropenia. Abnormal movement of lytic granules and reduced perforin content in cytotoxic T lymphocytes and natural killer cells account for their respective defects in cytolytic activity. It is likely that the investigation of the physiopathology of Hermansky-Pudlak type 2 syndrome will reveal nonredundant functions of this adaptor protein in the intracellular trafficking of membrane proteins.
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ABSTRACT: Natural killer (NK) cells are lymphocytes of the innate immune system that secrete cytokines upon activation and mediate the killing of tumor cells and virus-infected cells, especially those that escape the adaptive T cell response caused by the down regulation of MHC-I. The induction of cytotoxicity requires that NK cells contact target cells through adhesion receptors, and initiate activation signaling leading to increased adhesion and accumulation of F-actin at the NK cell cytotoxic synapse. Concurrently, lytic granules undergo minus-end directed movement and accumulate at the microtubule-organizing center through the interaction with microtubule motor proteins, followed by polarization of the lethal cargo toward the target cell. Ultimately, myosin-dependent movement of the lytic granules toward the NK cell plasma membrane through F-actin channels, along with soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent fusion, promotes the release of the lytic granule contents into the cleft between the NK cell and target cell resulting in target cell killing. Herein, we will discuss several disease-causing mutations in primary immunodeficiency syndromes and how they impact NK cell-mediated killing by disrupting distinct steps of this tightly regulated process.Frontiers in Immunology 01/2014; 5:2. DOI:10.3389/fimmu.2014.00002
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ABSTRACT: Primary hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease of hyperinflammation resulting from immune dysregulation due to inherited defects in the cytolytic machinery of natural killer and T cells. In humans, mutations in seven genes encoding proteins involved in cytolytic effector functions have so far been identified that predispose to HLH. However, although most affected patients develop HLH eventually, disease onset and severity are highly variable. Due to the genetic heterogeneity and variable time and nature of disease triggers, the immunological basis of these variations in HLH progression is incompletely understood. Several murine models of primary HLH have been established allowing to study HLH pathogenesis under more defined conditions. Here we directly compare the clinical HLH phenotype in six HLH-prone mouse strains with defects in the granule-dependent cytotoxic pathway. A severity gradient of HLH manifestations could be identified that is defined by the genetically determined residual lytic activity of cytotoxic T lymphocytes (CTL) and their ability to control lymphocytic choriomeningitis virus, which was used as a trigger for disease induction. Importantly, analysis of cohorts of HLH patients with severe bi-allelic mutations in the corresponding genes yielded a similar severity gradient in human HLH as reflected by the age at disease onset. Our findings define HLH as a threshold disease determined by subtle differences in the residual lytic activity of CTL.Frontiers in Immunology 01/2013; 4:448. DOI:10.3389/fimmu.2013.00448
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ABSTRACT: Adaptor protein-3 (AP-3) is a heterotetrameric complex, which regulates vesicular trafficking. Mutations of the b3A subunit cause the Hermansky–Pudlak syndrome type 2 (HPS-2), a rare genetic disease characterized byalbinism, platelet defects, and recurrent infections. Likewise, pearl mice, which lack functional AP-3, show several HPS-2 defects. The AP-3 absence results in defective TLR trafficking and signaling in dendritic cells (DC), but its effect on the efficiency of the in vivo antiviral response is unclear. We evaluated the impact of AP-3 deficiency on the distribution of DC subsets, interferon (IFN) production, and the susceptibility to murine cytomegalovirus (MCMV) infection. Pearl mice showed a distribution and frequency of conventional (cDC) and plasmacytoid DC (pDC) similar to that of wild-type mice both before and afterMCMV infection.Moreover, pearl mice controlled MCMV infection even at high virus doses and showed a normal production of IFN-a. Since pDC, but not cDC, from pearl mice showed an impaired IFN-a and tumor necrosis factor-a production in response to prototypic DNA (MCMV and Herpes Simplex virus) or RNA (Vesicular Stomatitis virus) viruses in vitro, it is likely that MCMV infection can be controlled in vivo independently of an efficient production of IFN-a by pDC, and that the AP-3 complex has a minimal impact on protective antiviral responses.Journal of Interferon & Cytokine Research 01/2015; 35(3):232-238. DOI:10.1089/jir.2013.0110 · 3.90 Impact Factor